To adjust the convergence you need to loosen and rotate/adjust the yoke not just adjust the purity rings.  Be careful what you touch if you attempt to converge the monitor which must be done while powered on, obviously.  It could be the yoke or tube is bad and won't converge properly then we need to trash it or call in the experts. Good luck!

Love me some head to head vs tennis...played it BITD and now on my own red tent.  Nothing like taking down the cpu when it is playing it's hardest--very difficult and fast play (and only 4player vs game). Next in order: Excitebike, SMB, Ice climber